Thermionic apparatus



June 11, 1929. SCHMIDT, JR 1,717,265

THERMI ONI C APPARATUS Filed July 19, 1927 Inventor: August SChTTlidt.JF.,

H is Attorney.

Patented June 11, 1929;

UNITED STATES 1,717,265 PATENT OFFICE.

AUGUST SCHMIDT, JR., OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK.

THERMIONIC APPARATUS.

My invention relates to thermionic a-pparatus provided with a cathode heating element and with exciting electrodes arranged to maintain the excitation of the apparatus when it is not loaded, and has for its principal object the provision of an improved apparatus and method of operation whereby the initial current of the heating element 1s kept within safe limits and theexcitation of the apparatus is readily established.

Various types of thermionic apparatus comprising a cathode which includes an activating material, such as barium oxide or the like, and provided with a heating element have been provided in the past. In the operation of many of these apparatus, difliculty is encountered-due to the fact that the cathode heating element tends to take a comparative- 1y large current at starting when it is cold and due to the further fact that the potential required to start ionization between the cathode and exciting electrodes is much larger than the potential requiredto maintain this ionization; In accordance with myinvention, these difiiculties are avoided by the provision of an impedance device which is so interconnected with the exciting and heating circuits of the apparatus as to limit the initial current of the heating element and cause a comparatively high voltage to be applied to the exciting electrodes when they are first energized.

My invention will be better understood from the following descri tion when considered in connection with t e accompanying drawingand its scope will be pointed out in the appended claims.

The drawing is a wiring diagram of an alternating current rectifying system wherein my invention has ben embodied.

This system comprises an alternating current circuit 1 and a direct current circuit 2 which are interconnected through a transformer 3 and a thermionic device 4 provided with a heating element 5, a tubular cathode 6 4 anodes 7 and exciting electrodes 8. V The container of the device 4 is preferably i freed from moisture, is evacuated to the degree required for the production of a substantially pure electron discharge therein and is then supplied'with a suitable gas at a pressure below that at which the discharge becomes arc-like and tends to concentrate or become localized on the cathode. For example, mercury vapor, a. rare gas such as 1927. Serial No. 206,954.

argon or neon or a mixture of rare gases may be utilized as the ionizable medium. As previously indicated, the cathode 6 may be coated with a material having a higher electron emissivity than the cathode metal.- Among the activating materials which may be utilized are barium oxide, other alkaline earth oxides, or rare earth metals such as cerium.

The transformer 3 comprises a secondary winding 9 provided with end terminals which are connected to'the anodes 7 and with an intermediate terminal which is connected to the negative terminal of the direct current circuit 2. The positive terminal of the circuit 2 is connected to the cathode 6.

Current is supplied to the cathode heating element 5 and to the exciting electrodes 8 through an impedance device shown as a high reactance transformer 10 which is provided with a three-legged core 11, a primary winding 12, a secondary winding 13 connected to the heating element 5, and a secondary wind ing 14 connected between the heating element 5 and the exciting electrodes.

With these connections, the magnitude of the current supplied to the heating element 5 before it has become heated islimited to a comparatively low value due to the fact that the reactive drop of the winding 13 causes a comparatively large part-of the core flux to be shunted through the middle leg.- A comparatively high voltage is thus applied to the exciting electrodes 8 due to the flux shunted through the coil v14: when the heating element is cold and the heating current tends to be highest. The heating current is thus maintamed within safe limits at starting and the exciting electrodes are subjected to a comparatively high voltage which ensures that ionization is established between the cathode 6 and the exciting electrodes 8. As the heating element comes up to its normal operating temperature, its current decreases'and the potential of the exciting electrodes 8 is decreased due to the resulting decrease in the flux of the coil 14.

With the connections illustrated, the exciting current of the device iis dependent on the electron emissivity of the heating element 5. It will beapparent that the intermediate terminal of the winding 14 may be connected to the cathode 6 instead of to the intermediate terminal of the secondary windin 13, so that lized for producing the exciting current. As indicated by the dotted lines at the bottom of the middle leg of the transformer core, this leg may be provided with an air gap for ensuring that the reaetance of the transformer 10 is sufficiently high.'=

The embodiment of the invention illustrated and described herein has been selected for the purpose of clearly setting forth the principles involved. It will be apparent, however, that the invention is susceptible of being modified to meet the different conditions encountered in its use and I therefore aim to cover by the appended claims all modifications within the true spirit and scope of my invention.

What I claim as new and desireto secure by Letters Patent of the United States is:

1. The combination of an impedance device comprising a core and a plurality of windings wound upon said-core, and a thermionic apparatus provided with a cathode heating element connected to one of said windings and with an exciting electrode connected to said heating element through means comprising said winding and another of said windings. v

2. The combination of an impedance device comprising a core and a plurality of windings each wound .on a different leg of said core, and a thermionic apparatus provided with a cathode heating element and with an exciting electrode arranged to'be subjected to a voltage applied through another of said windings.

3. The combination of a transformer comprising a core and a plurality of secondary windings connected to one another at points intermediate their ends, and a thermionic apparatus provided with a cathode heating elesaid windings and with exciting electrodes connected between the ends of another of said windings.

4. The. combination of an impedancedevice comprising a core and a plurality of windings wound on different legs of said core and interconnected at points intermediate their ends, and a thermionic device comprising a cathode, a heating element mounted in proximity to said cathode and connectcdbetween the ends of one of said windings, and a .pair of exciting electrodes connected between.

, citing electrode for limiting the starting current of said element.

In witness whereof, I have hereunto set my hand this 18th day of July, 1927.

AUGUST SCHMIDT, JR.

- ment connected between the ends of one of 

